People who claim their free bus pass after the age of 60 are more active when they leave the house, enabling them to stay fitter than people who use their cars to get around.

Walking or cycling to and from the bus stop every day can help maintain people's physical and mental health in their later years and lower the risk of injury or illnesses like heart disease, researchers explained.

The new study of data from the UK National Travel Survey found that over-60s who hold a free bus pass were more likely to use "active" modes of travel such as walking, cycling or catching the bus.

Researchers studied information on 17,000 people who answered a questionnaire about their means of travel and compiled a one-week "travel diary" at some point between 2005 - the year before free bus passes for everyone over 60 were introduced - and 2008.

Bus pass holders were almost four times more likely to undertake any "active" travel during the week they kept their diary, and were 15 per cent more likely to report walking three or more times per week.

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Aside from having a bus pass, the other major factor which prevented people from using the bus, walking or using any other form of "active" transport was having a car, the study found.

People living in towns and cities were more likely to use active modes of transport, due to better provision of services, while people in rural areas were more likely to walk frequently.

Previous research has shown that one in five adults in Britain meets the recommended health target of 30 minutes' exercise, five times a week, simply by getting around each day.

Getting 15 minutes of moderate exercise each day has already been shown to lower the risk of early death from any cause in over-60s by 12 per cent.

Sophie Coronini-Cronberg of Imperial College London, who led the new study, said even "incidental" exercise like walking to the bus stop could lower the risk of health problems in older people.

Writing in the American Journal of Public Health, she said: "Remaining physically active is as important in older as in younger adults because it reduces the risk of loss of mobility and muscle strength, falls and fractures, and and promotes social and mental well-being.

"By swapping private vehicle travel for public transport - which may involve walking or cycling to transport access points or interchanges - physical activity levels are raised, offering significant health benefits, such as a reduced risk of obesity and cardiovascular ill health."

Free bus passes for people over 60 were introduced for local transport in England in 2006, and the programme was broadened two years later to apply to all local buses anywhere in the country.

But politicians have since argued the scheme, which costs £1.1 billion per year, to be cut or amended to relieve public spending pressure.

Nick Clegg claimed last December that bus passes should be means-tested, with better-off elderly people making a "sacrifice" to help reduce government debt.

Ms Coronini-Cronberg said the government should consider the health benefits of the bus pass scheme before deciding whether it represents value for money.

She wrote: "Despite pensioners having more free time than working adults, most fall short of achieving nationally recommended levels of physical activity and may gain weight during retirement.

"Although the costs of the scheme are considerable, it may offer value for money as it seems to promote physical activity among older people, thereby helping to reduce inactivity-related mortality and morbidity."